In a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, a network side uses a PBCH to send a cell broadcast message that includes a master information block (MIB). The MIB has a total of 24 bits, including three bits for a system bandwidth. The three bits indicate one of six bandwidths: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. The MIB also includes one bit for physical hybrid automatic repeat request indicator channel duration (PHICH-duration), which indicates a normal or extended PHICH-duration. The MIB also includes two bits for a PHICH-resource corresponding to a PHICH parameter Ng={1/6,1/2,1,2}. The MIB also includes eight bits for a system frame number (SFN), where the eight bits are eight most significant bits of the SFN. The MIB also includes 10 reserved bits. After a cell search procedure, a terminal device achieves subframe synchronization and frame synchronization using a synchronization signal. That is, a terminal device learns of a location of a subframe 0 in a radio frame using the synchronization signal. A PBCH is on first four orthogonal frequency division multiplexing (OFDM) symbols in a second timeslot (slot) in a subframe 0 in time domain, and occupies 72 central subcarriers in frequency domain. The PBCH is sent repeatedly for four times within a 40-ms transmission time interval (TTI). One PBCH is sent every to ms. The sent PBCHs carry same and self-decodable coded bits. Therefore, when a signal-to-interference ratio (SIR) is high enough, the terminal device can successfully decode PBCH content by receiving only one of the PBCHs sent within 40 ms. If decoding fails, the terminal device performs decoding by softly combining a current PBCH and a PBCH sent at a next to ms, until the terminal device successfully decodes the PBCH. In LTE, an SFN has a length of to bits. In a MIB broadcast by a PBCH, only the first eight bits of an SFN are broadcast, and the two remaining bits are determined based on a location, in a 40-ms period window, of a frame in which the PBCH is sent. Two least significant bits of an SFN on a PBCH in a first 10-ms frame within the 40 ms are 00; two least significant bits of an SFN on a PBCH in a second 10-ms frame within the 40 ms are 01; two least significant bits of an SFN on a PBCH in a third 10-ms frame within the 40 ms are 10; and two least significant bits of an SFN on a PBCH in a fourth 10-ms frame within the 40 ms are 11. Within each 40 ms when a base station sends PBCHs, the base station uses four different phases of a PBCH scrambling code to represent different occasions. Different phases correspond to different 10-ms frames. In other words, two least significant bits of an SFN corresponding to one phase are different from two least significant bits of an SFN corresponding to another phase. In addition, the scrambling code is reset every 40 ms. After receiving the PBCH, the terminal device attempts to decode the PBCH using each of the four phases. If decoding succeeds, the terminal device knows in which 10-ms frame within 40 ms the base station sends the PBCH, determines the two least significant bits of the SFN based on a mapping relationship between the four different phases of the scrambling code and the two least significant bits of SFNs, and finally determines all the to bits of the SFN.
In a fifth generation (5 Generation, 5G) system, a higher spectrum band is used than a spectrum band used in LTE. Therefore, radio signal transmission attenuation increases, and radio signal coverage reduces. In this case, a beamforming technology of massive multiple-input multiple-output (massive MIMO) is used by using a plurality of antennas of a base station to obtain high antenna gains, so as to complement path losses. Multi-beam transmission is supported for synchronization signals and PBCHs in 5G, to facilitate reception of terminal devices in a cell. Multi-beam transmission of synchronization signals (SS) is implemented by defining an SS burst set. One SS burst set includes one or more SS bursts, and one SS burst includes one or more SS blocks. One SS block carries a synchronization signal of one beam. Therefore, one SS burst set includes synchronization signals of beams that are of a same quantity as SS blocks in the cell. One SS block includes one symbol for a primary synchronization signal (PSS), one symbol for a secondary synchronization signal (SSS), and two symbols for PBCHs. The SSS may be used as a demodulation reference signal for the PBCH. An SS burst set sending periodicity includes a default 20-ms periodicity and network-indicated periodicities. The network-indicated periodicities include 5 ms, to ms, 20 ms, 40 ms, 80 ms, and 160 ms. In 5G, a PBCH is sent in an SS block, and a PBCH ITI is 80 ms. Therefore, within 80 ms, the base station may send 4 PBCHs at the default 20-ms SS block sending periodicity, or may send 16 PBCHs at an indicated 5-ms SS block sending periodicity, or may send eight PBCHs at an indicated 10-ms SS block sending periodicity, and so on.
In a 5G system, because a PBCH is sent in an SS block while there are a plurality of SS block sending periodicities, including the default periodicity and the network-indicated periodicities, the PBCH is no longer sent at a fixed interval of to ms as in LTE. Therefore, in 5G, a solution is needed how to use a PBCH to indicate an SFN of a radio frame in which the PBCH is located.